From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Wed, 25 Mar 2020 12:02:26 +0000 (+0000)
Subject: drm/i915/execlists: Pull tasklet interrupt-bh local to direct submission
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=6670b413f8452ec303efcd2f9a6009c8602a297e;p=linux.git

drm/i915/execlists: Pull tasklet interrupt-bh local to direct submission

We dropped calling process_csb prior to handling direct submission in
order to avoid the nesting of spinlocks and lift process_csb() and the
majority of the tasklet out of irq-off. However, we do want to avoid
ksoftirqd latency in the fast path, so try and pull the interrupt-bh
local to direct submission if we can acquire the tasklet's lock.

v2: Document the read of pending[0] from outside the tasklet with
READ_ONCE.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200325120227.8044-1-chris@chris-wilson.co.uk
---

diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
index f88d3b95c4e10..d49baade09862 100644
--- a/drivers/gpu/drm/i915/gt/intel_lrc.c
+++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
@@ -2891,6 +2891,13 @@ static void __submit_queue_imm(struct intel_engine_cs *engine)
 	if (reset_in_progress(execlists))
 		return; /* defer until we restart the engine following reset */
 
+	/* Hopefully we clear execlists->pending[] to let us through */
+	if (READ_ONCE(execlists->pending[0]) &&
+	    tasklet_trylock(&execlists->tasklet)) {
+		process_csb(engine);
+		tasklet_unlock(&execlists->tasklet);
+	}
+
 	__execlists_submission_tasklet(engine);
 }